There have been a great deal of efforts to translate a document automatically on a machine since 1940s with the advent of the computer. Machine-translation systems of early days such as Georgetown Automatic Translation (also known as GAT) and Traduction Automatique à l'Université de Montréal (also known as TAUM) are regarded as pioneers in this field but their translation quality fell badly short of the industry's expectations.
With the recent rapid development of computer capabilities and the increasing need to resolve the information blockage due to language barriers, however, research works in artificial intelligence and computational linguistics have made significant progresses, giving rise to the modern development of machine translation. In a machine-translation system, the method applying translation memory plays the central role.
There are two types of applying translation memory in a machine-translation system: exact match and approximate match. If the first type is employed, a translated sentence may be produced only when there is an exact match between the input sentence and the translation memory. In this case, the quality of translated sentence is expected to be high. If the second type is employed, a translated sentence may be produced in spite of an inexact match with the translation memory, if it is regarded as being sufficiently close to the translation memory based on the degree of approximation.